Probably invented in the 16th century, the carpenter's rule was a device to help a man who could not multiply to find the area or the volume of his timber. In its original form, it gave at a glance either the length to make a square foot of a board of given width, or the length to make a cubic foot of a piece of square (or equivalent square) cross-section.

This is a guide to help an inexperienced collector identify trade tools. The word "trade" encompasses a wide range of activities – but for the purposes of this article, trade tools are considered to be implements or devices that augment our dexterity to accomplish a task or to carry out a job.

This account sets down most of what is known on this topic and has been written in the hope of obtaining some useful feedback. Bath stone is a relatively soft oolitic limestone of Jurassic age, Its older name of freestone means it can be freely worked by hand tools; there is no plane of cleavage.

When the spire of Salisbury Cathedral was completed in about 1310 it was the tallest stone structure in Europe and it remained so for a hundred and fifty years. After the demise of Lincoln and Old St. Pauls it was the tallest building in England.